1. Field of the Invention
The present invention relates to a method for manufacturing capacitors, particularly to a method for manufacturing DRAM capacitors.
2. Description of Related Art
With the increasing of integrality of integrated circuits and the decreasing of device size, the surface of a memory cell must be narrowed down to manufacture a high density DRAM. Thus, the surfaces of electrodes storing charges are also decreased, resulting in capacitors that provide insufficient capacitance. Therefore, it is very urgent to solve the problem of insufficient capacitance. There are basically two types of conventional methods for increasing the capacitance: (1) stacked capacitors (STC), and (2) trench capacitors. The former type of capacitors usually utilize materials with high dielectric constant such as tantalum oxide (Ta.sub.2 O.sub.5), barium oxide (BaO), strontium oxide (SrO), or titanium oxide in place of conventional dielectric materials such as silicon oxide nitride to decrease the thickness of the dielectric layers.
The stacked capacitor requires complex processes to form hemispherical or cylinder shaped surfaces on one electrode of the capacitor to enhance its effective surface; however, this also enhances the nonplanarity of the wafer. Moreover, the manufacturing processes for such the newly devised dielectric materials used herein are still being developed, and such the properties as leakage, thermal stability and so on need to be further improved. The advantage of the trench capacitor is that the wafer surface is much more plane after the capacitors finished. Moreover, the processes for dielectric materials used therein, such as nitride or oxidated nitride, have been well developed. However, it requires deep trenches to provide sufficient capacitance, therefore the aspect ratio could be more than 30, which increases the difficulties of etching and trench filling.
In order to overcome the disadvantages of conventional processes described above, this invention provides a modified method for manufacturing DRAM capacitors. By increasing the surface area of a storage electrode without changing the margin of a memory cell, the capacitance of a DRAM capacitor is increased. Thereby, a high density DRAM with high capacitance can be obtained.